1. Field of the Invention
The present invention relates to a flat lamp for emitting light to a surface area, and more particularly to a liquid crystal display using a flat lamp for emitting light to reduce delay time for lamp turn-on despite low voltage and to extend life-span of the lamp.
2. Background of the Related Art
Generally, lamps are classified into two categories according to the principles of generating light used as a light source: glow lamps and fluorescent lamps. A flat lamp belongs to the fluorescent lamps category since the flat lamp generates visible light rays by fluorescence in which ultraviolet rays produced by glow discharge within the lamp stimulate fluorescent materials.
Presently, flat lamps are implemented as light sources for liquid crystal display (LCD) devices. Since LCD devices are non-luminous and display images by controlling the amount of light transmitted through a liquid crystal layer, LCD devices need additional light sources, i.e., backlight assemblies, for displaying images.
Exemplary light sources used for backlight assemblies may be classified into different categories: a point light source of a white halogen lamp, a linear light source of a fluorescent lamp, a plane light source of an electro-luminescent (EL) device or light emitting diode.
However, the light source used in conventional backlight assemblies is a linear light source using a cold cathode fluorescence lamp (CCFL) that requires additional features such as a light guiding plate, a diffusion plate, and a prism sheet, for example, for producing a uniform plane of light to a display surface.
An exemplary solution to solve the above problem is a flat lamp enabled to uniformly emit light to a surface area a planar light source.
One example of a flat lamp for emitting light to a surface area is disclosed in U.S. Pat. No. 5,777,431, which is explained hereinafter.
FIG. 1 shows a plan view of a flat lamp for emitting light to a surface area according to U.S. Pat. No. 5,777,431, wherein the cover is omitted.
As shown in FIG. 1, a volute channel 6 is formed by an internal bulkhead 3 and an external bulkhead 2, wherein the internal bulkhead 3 has a same height as the external bulkhead 2 from a rectangular bottom 1. A cathode 4 emitting electrons is placed at an end of the internal bulkhead 3 that adjoins with the external bulkhead 2. An anode 5 is disposed at a center portion of the bottom 1 and a gas is injected into the channel 6 for arc-discharging. The volute channel 6 has a spiral shape that terminates at a center portion of the bottom 1, whereby electrodes emitted from the cathode 4 travel toward the anode 5 in a counterclockwise direction.
In the flat lamp of FIG. 1, an electric field is generated when an electric potential is applied between the cathode 4 and the anode 5, whereby electrons are emitted from the cathode 4 to the anode 5. Accordingly, the electrons emitted from the cathode 4 migrate along the volute channel 6 and emit ultraviolet rays as a result of impacting with the arc-discharging gas. The ultraviolet rays then stimulate the fluorescent material to produce a glow discharge, thereby producing visible rays. Namely, the visible rays are emitted through the cover (not shown in the drawing) that is located at the tops of the internal bulkhead 3 and the external bulkhead 2 and disposed to overlie the entire surface area in which the channel is formed. As mentioned above, the flat lamp is used as an independent illuminator and as a backlight assembly when placed at a rear portion of a LCD device panel.
Unfortunately, the flat lamp has the cathode 4 and the anode 5 disposed at opposite ends of the volute channel 6. Accordingly, the flat lamp requires a long response time for producing visible light during the turning-on interval and requires a high voltage for sufficient luminescence. Such a high voltage inevitably reduces the life-span of the electrode of the cathode 4 and the anode 5, and hence, reduces the life-span of the flat lamp. Moreover, the total length of the volute channel 6 ultimately limits the total size of the lamp.